5V DC Regulation for Sensor Protection

Question

I am trying to design a driving board for a spectrometer, which requests 5V constant DC supply. Due to its sensitivity, I want to make sure about the voltage provided to the sensor. The supply is going to be provided from an embedded board (e.g., Beaglebone Blue). Is there any reason why I should add any regulation component(s)? Should I add a voltage regulator or a zener diode?

Thank you.

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First, regarding the voltages provided, I could also have 3V3 available provided from the main board. Would it be better to provide 3V3 and add a boost converter to 5V or provide 5V and add a crowbar circuit? Which are the pros and cons of each solution?

Also, regarding the fuse at the start of the crowbar circuit (please refer to the image attached, which I have taken from the TL431 Texas Instruments datasheet), wouldn't it cause a voltage drop from the 5V provided? Is there another point of the crowbar circuit where I could place the fuse?

Answer 1

You need to know how much noise/ripple the spectrometer can tolerate, and how much the 5V supply you use generates. Then, you'll know if they are compatible.

If your spectrometer requires 5V and all you have is a 5V supply, you won't be able to add a regulator though. At most a LC filter. So depending on the noise/ripple requirements, you might have to start with a higher voltage supply and add a local regulator. Can't tell without more data.

Now, if you want to protect against reverse polarity and overvoltage, starting with a higher voltage makes things much easier: just add a diode and a regulator.

Starting from 5V...

• Put a polyswitch in the supply, acting as a resettable fuse.
• Put a diode in reverse across the supply, so it will short it out and trip the polyswitch if it's plugged in reverse.
• Put something like a TL431 wired as a precision shunt regulator across the supply, or even a simple zener, triggering a thyristor crowbar to short the supply and trip the polyswitch.

There are simpler solutions, like this one-chip USB overvoltage protector which lets the power through only if it is correct.

...And don't forget to check if the IO needs protection too!